Current measurement is a measurement task which is frequently set. In automotive systems, for example, there is often the need for a current measurement, in particular for the purpose of receiving sensor information which has been modulated onto current signals or else for the purpose of detecting overload conditions in power output stages.
Known solutions usually use a resistor (shunt resistor) and an amplifier circuit which operates in continuous-time mode and is intended to amplify the current-dependent voltage drop across the resistor. The voltage drop across the resistor is often problematic and undesirable since it causes feedback to the system which provides the current to be measured. In the case of a current measurement with the aid of a so-called sense field-effect transistor (FET), in particular, a shunt resistor in the current path of the sense FET results in undesirable negative feedback which results in the sense FET and the power FET connected to the latter operating at different operating points and the current measurement thus being falsified.
One possible measure for reducing the influence of the shunt resistor may be to keep the resistance value of the shunt resistor as low as possible. In this case, the offset voltage of the amplifier needed to amplify the voltage across the shunt resistor is then the dominant cause of measurement errors. In order to keep the offset voltage of the amplifier as low as possible, bipolar transistors are often used in the input stage of the amplifier in known current measurement methods. As the integration density increases, the use of bipolar components becomes uneconomical on account of the large amount of chip area required.
There is thus a need for a current measurement method which causes a small voltage drop in the current path of the measurement current and in which the offset voltage of the amplifier used no longer has a significant effect on the accuracy of the current measurement.